"That's how long it will take the spacecraft to make its automated parachute- and rocket-powered descent to the frigid Martian surface," wrote William Harwood in yesterday's story on Spaceflight Now.

Touchdown is expected at 7:53:52 p.m., Earth-receive time.

The actual landing will have occurred 15.3 minutes earlier, but it will take that long for radio signals, traveling at 186,000 miles per second, to reach flight controllers on Earth.

At a news briefing last week, Ed Weiler, NASA's chief of science operations, after listing in detail past catastrophes involving Mars landers and the myriad things that could go wrong this evening, summed it up by saying, "I hope I've convinced you this is no trip to grandma's for the weekend."